INVITED REVIEWDiabetic kidney disease in the db/dbmouse - 《American Journal of Physiology》美国生理学杂志干细胞之家



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发表于 2009-4-21 13:38 |只看该作者 |倒序浏览 |打印

作者：KumarSharma, PeterMcCue,  Stephen R.Dunn作者单位：1 Dorrance Hamilton Research Laboratory, Division ofNephrology, Department of Medicine, and Department ofAnatomy, Cell Biology and Pathology, Thomas Jefferson University,Philadelphia, Pennsylvania 19107

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      【摘要】
   Diabetic nephropathy isincreasing in incidence and is now the number one cause of end-stagerenal disease in the industrialized world. To gain insight intothe genetic susceptibility and pathophysiology of diabetic nephropathy,an appropriate mouse model of diabetic nephropathy would be critical. Alarge number of mouse models of diabetes have been identified and theirkidney disease characterized to various degrees. Perhaps the bestcharacterized and most intensively investigated model is the db / db mouse. Because this model appears toexhibit the most consistent and robust increase in albuminuria andmesangial matrix expansion, it has been used as a model of progressivediabetic renal disease. In this review, we present the findings fromvarious studies on the renal pathology of the db / db mouse model of diabetes in the context ofhuman diabetic nephropathy. Furthermore, we discuss shortfalls ofassessing functional renal disease in mouse models of diabetic kidney disease.
      【关键词】 diabetic nephropathy creatinine albuminuria mesangialmatrix8 ]5 Q& f3 I3 n, o: j$ E1 x& z
   INTRODUCTION

THE db / db MOUSE wasidentified initially in 1966 in Jackson Labs as an obese mouse that washyperphagic soon on weaning ( 13 ). The diabetic gene( db ) is transmitted as an autosomal recessive trait. The db gene encodes for a G-to-T point mutation of the leptinreceptor, leading to abnormal splicing and defective signaling of theadipocyte-derived hormone leptin ( 1, 15 ). Lack of leptinsignaling in the hypothalamus will lead to persistent hyperphagia andobesity with consequently high leptin and insulin levels. Therecognition of diabetes initially was recognized in mice from theC57BLKS/J strain. The C57BLKS/J mouse shares 84% of its alleles withthe common C57BL/6 strain and 16% with the DBA/2J strain and wasinitially maintained by Dr. N. Kaliss (KS). The updated nomenclaturefrom Jackson Labs uses the term C57BLKS/J Lepr (KS forKaliss) to designate the db / db mouse in the C57black Kaliss background (Jackson Labs, http://jaxmice.jax.org/jaxmicedb/html/model_66.shtml ). For thepurpose of this review, the common name db / db will be used.8 v' B5 |4 {; `3 K# B7 _# ]( g

The natural history of diabetes and the renal manifestations in the db / db mice have been described primarily in theC57BLKS/J strain. In the C57BL/6J background, less hyperglycemia isfound despite similar degrees of hyperphagia and weight gain( 12 ). This may be attributed to the development ofpancreatic islet cell hypertrophy in the C57BL/6J background ratherthan islet cell degeneration, as seen in the C57BLKS/J background( 12 ). Another obese, diabetic mouse is the ob / ob mouse. This ob / ob mouse differs from the db / db mouse in that it hasa deficiency in the production of leptin but intact leptin signaling.Similar to the db / db mouse, the ob / ob mouse in the C57BLKS/J background develops -cell atrophy and severe hyperglycemia, whereas ob / ob mice in the C57BL/6J background develophyperplasia of the pancreatic ducts and only mild hyperglycemia( 12 ). Interestingly, the C57BLKS/J mouse is moresusceptible to the effects of the -cell toxin streptozotocin compared with the C57BL/6J strain ( 20 ). Thus severesusceptibility to diabetes appears to be present in the KS backgroundand may be independent of the underlying trigger for islet dysfunction. The renal disease in ob / ob mice primarilyconsists of diffuse and nodular lipohyaline changes in glomeruli( 34 ). The relative paucity of diabetic renal lesions inthe ob / ob mouse, compared with the db / db mouse, may be due to lack of circulatingleptin, as leptin has been found to directly stimulate matrixproduction ( 10 ); however, part of the difference may bedue to the different backgrounds of the mice that have been studied.

In the C57BLKS/J db / db mouse, hyperinsulinemia isnoted by 10 days of age and blood glucose levels are slightly elevatedat 1 mo of age (7.2 ± 2.3 mM) ( 17 ). After 1 mo ofage, the db / db mice are distinguished fromwild-type and heterozygous mice by the presence of increased fatdeposition in the inguinal and axillary regions. The db / db mouse develops frank hyperglycemia withglucose values of 9.7 ± 1.6 mM by 8 wk of age and 15.7 ± 4.3 mM at 10 wk of age ( 17 ). There is a progressiveincrease in food and water intake associated with progressive weightgain until 4-5 mo of age. Food intake averages ~40 g/wk betweenthe ages of 4 and 16 wk of age. Water intake averages ~30 ml/wkbefore the onset of hyperglycemia and increases to 100 ml/wk withworsening hyperglycemia ( 17 ). Progressive hyperglycemia isnoted with mean levels of glucose of 28.6 ± 13.2 mM and peaklevels reaching as high as 44 mM at 16 wk of age ( 17, 19 ).After 5-6 mo of age, the body weight and insulin levels begin tofall in association with pancreatic islet cell degeneration( 12 ). By this time, the mice become so obese that theyhave difficulty ambulating in the cage and obtaining food and water.The cause of death is not clear, although ketonuria, hematuria, andgastrointestinal bleeding have all been noted during the terminal stage( 13 )." {5 M5 Q* ]  y5 V
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RENAL HYPERTROPHY1 }5 g7 S( B5 d+ i

At the tissue level, several studies measured renal size in the db / db mouse. An important caveat is because alarge amount of fat envelops the kidneys, to ensure accurate weight,careful removal of fat tissue is required before weighing of thekidneys. Table 1 lists the results ofvarious kidney parameters that have been reported from severalpublished studies. Evidence of kidney hypertrophy has been noted in db / db mice at the age of 16 wk ( 6, 11, 35 ). Surprisingly, the kidney weights in the diabetic mice donot remain significantly increased above control values between theages of 21 and 25 wk (Table 1 ) ( 14 ). In 22-wk-old malemice, we found that the right kidney is significantly heavier than theleft kidney in the db / db mice (right 248 ± 6 vs. left 208 ± 7 mg, P On the basis of the above, renalhypertrophy should be evaluated before 16-20 wk of age and bothkidneys should be weighed individually.
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Table 1. Renal parameters in C57BLKS/J Lepr (db/db and db/m) mice atvarious ages
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GLOMERULAR HYPERTROPHY- E( o6 M: r: s1 t, H
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Glomerular surface area has been measured using standardmeasurements of glomerular tuft areas using a digital planimeter atvarious ages of the db / db and db / m mice (Table 1 ). Cohen et al.( 4 ) found that glomerular surface area in nonperfusedkidneys was increased by 23% at 8 wk of age and remained increased by 27% at 16 wk of age. Koya et al. ( 14 ) studied glomerularsurface area in perfused db / db mouse kidneys at25 wk of age and also found a significant increase (Table 1 ). Althoughthe absolute values of the glomerular surface area were over twofoldgreater in perfused kidneys ( 14 ), compared withnonperfused kidneys ( 4 ), the degree of glomerularhypertrophy in the db / db group was similar (22 and 27% in both studies). Glomerular hypertrophy at the onset ofdiabetes may be due to alteration of glomerular hemodynamics as thereis evidence of glomerular hyperfiltration in db / db mice during the early stages of diabetes( 8 ). However, there have not been any studies ofglomerular capillary pressures in db / db mice andthe contribution of capillary loop enlargement and cell hypertrophy ofthe different glomerular cell compartments has not been evaluated.& p5 V: v; R4 b3 Z; ~, R% U6 c

GLOMERULAR PATHOLOGY
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An in-depth characterization of renal pathology in the db / db mouse was first described by Like andcolleagues ( 21 ) in 1972. In this initial study, mice werestudied at various time intervals, with some mice having their foodrestricted between weeks 7 and 11 to allow themice to live to 12-22 mo of age. Gross examination did not revealany differences in the kidney, although calyceal dilation andflattening of the papilla were notable in diabetic mice older than5-6 mo of age. Before the onset of sustained hyperglycemia (4-6 wk of age), the glomeruli of mice were not distinguishable from their nondiabetic littermates. By 5-6 mo of age, diabetic mice had larger glomeruli with increased mesangial matrix by periodic acid-Schiff (PAS) staining. By 18-20 mo of age, the mesangial matrix and glomerular enlargement became more pronounced and thickening of the glomerular basement membrane (GBM) was notable. Nodular lesionsof the subepithelia basal lamina were also noted, which were PASpositive. It should be noted that the described subepithelial noduleswere distinct from the Kimmelstein-Wilson nodules described in humandiabetic nephropathy. By electron microscopy (EM), the finding ofincreased mesangial matrix with frequent foci of vacuolar change andembedded collagen fibrils was found to distinguish older diabetic mice(5-6 mo of age) from nondiabetic littermates. GBM thickening andsubepithelial nodularity were noted primarily in diabetic mice olderthan 12 mo of age. In the oldest diabetic mice studied (16-22 moof age), strikingly large subepithelial nodular densities were observedalong with foot process fusion. Subsequent studies of diabetic renalpathology were performed in the early 1980s by Lee and colleagues( 16-19 ). By morphometric analysis of glomeruli,mesangial matrix enlargement was consistently noted after the age of 16 wk in the db / db mouse. When db / db mice were placed on caloric restriction bylimiting their time of feeding to 3 h/day, their body weight and theblood glucose levels were only slightly higher than the heterozygouscontrol ( db / m ) mice, and renal pathology wasprevented ( 17 ).+ n3 I. D$ {% G; L# a7 D6 T

A reappraisal of renal pathology in db / db mice byseveral groups in the past decade has brought renewed recognition ofthis mouse model as a useful tool for the study of diabetic nephropathy.
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MESANGIAL MATRIX EXPANSION2 S" @' o$ C* w( Z
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Diffuse expansion of the mesangial matrix is considered to be thehallmark pathological feature of established diabetic nephropathy inhumans ( 24, 25, 29, 32 ). Of the many mouse models of diabetes that have been identified, the db / db mouse appears to most closely mimic the progressive nature of mesangialmatrix expansion seen in human diabetic nephropathy. The time course ofmesangial matrix expansion was described recently by Cohen et al.( 4 ) (Table 1 ). At 8 wk of age, before the onset of severehyperglycemia, there is no discernible increase in the mesangialcompartment of the db / db mouse. At 12 wk of ageand after 4-6 wk of hyperglycemia, a twofold increase in mesangial matrix was noted. After 16 wk of age, a consistent threefold increase in mesangial matrix expansion was reported by several independent studies ( 4, 6, 14, 35 ) (Table 1 ). Although many of theprior studies were performed without perfusion of the mouse kidneys,the study by Koya et al. ( 14 ) showed a similar increase inmesangial matrix expansion in perfused kidneys from db / db mice of 25 wk of age.( ^7 u- r3 K  O0 f7 u

Selected images of PAS-stained glomeruli from db / m and db / db male mice of21 wk of age are presented in Fig. 1. Inthe normal heterozygous mouse (C57BLKS/J db / m ),the outer cortical glomerulus is of normal size and configuration (Fig. 1 A ). Bowman's capsule is of the usual caliber, and there isno epithelial cell proliferation. The capillary tuft is fully expandedwith patent capillary loops, and the GBMs appear thin and delicate. Themesangium contains the usual complement of cells and matrix withoutmatrix expansion, inflammation, or sclerosis. In distinction, the mostseverely affected glomerulus from a db / db mousekidney shown appears dramatically different (Fig. 1 B ). Thevisceral epithelial cells are swollen and appear prominent. Theglomerular capillary basement membranes appear thickened, and theperipheral capillary loop appears collapsed. The mesangium is diffuselyand markedly expanded with PAS-positive matrix material. The overallcellularity is normal without inflammation or necrosis. Approximately30% of glomeruli have a similar appearance, and the remaining have alesser degree of mesangial matrix expansion. Thus, by light microscopy,the appearance is very similar to moderate human diabetic nephropathyat the glomerular level. However, there was no evidence ofKimmelstein-Wilson lesions and capsular drop lesions were only rarelyseen. By EM analysis, segmental GBM thickening has been reported byseveral studies ( 11, 21, 22 ). However, formal quantitativestudies have not been published to establish the degree of GBMthickening.
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Fig. 1. Light microscopic appearance of glomeruli from malenondiabetic control ( db / m ) mice ( A )and diabetic ( db / db ) mice ( B and C ) at 21 wk of age. There is diffuse mesangial matrixexpansion ( B ) and evidence of arteriolar hyalinosis( C ) in db / db mice. Renal tissue wasfixed with 10% neutral buffered formalin, and 4-µm sections werestained with periodic acid-Schiff. Images are taken at ×400magnification.# i( H+ v+ d& S- Q0 B( C
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The constituents of the mesangial matrix expansion in the db / db mouse kidney consist of increased type IVcollagen, fibronectin, and laminin ( 6, 9, 14, 30, 35 ). ByNorthern blot analysis of renal cortex, a two- to eightfold increase intype IV collagen [ 1(IV)] gene expression and a fourfold increasein fibronectin gene expression appeared at 16 wk of age ( 6, 30, 35 ). By immunostaining, a marked increase in fibronectin andtype IV collagen was described in glomeruli of db / db mice at 25 wk of age ( 14 ). Laminin isoforms- 1 and - 5 were found to be increased in glomeruli of db / db mice by immunostaining; however, themRNA levels were decreased in the renal cortex at the same time points( 9 ). In human diabetic nephropathy, the increase inmesangial matrix expansion has also been associated with an increase infibronectin, 1(IV) and 2(IV) collagen chains, and laminins( 28 ). Thus a very similar pattern of the components ofmesangial matrix that account for the expansion in human diabeticnephropathy has been noted in the db / db mouse.

IMMUNOFLUORESCENT STUDIES4 p$ `0 f. R% x2 A. S: _

Several studies observed diffuse uptake of IgG, IgA, IgM, andcomplement in glomeruli of db / db mice at as earlyas 8 wk of age ( 16-19 ). On the basis of thestudy by Like et al. ( 21 ) with older db / db 8 mo of age), the presence ofsubepithelial nodular deposits under EM may represent immune complexes.However, such lesions have not been described on EM analysis in the db / db mouse at 16 wk of age ( 11 ). Itshould also be noted that nondiseased mice from various backgrounds mayexhibit glomerular binding of immunoglobulins, including IgG, IgM, andIgA ( 23 ). The degree of immune complex deposition can bereduced if they are raised in germ-free environments ( 23 ).Therefore, the increased glomerular immunglobulin uptake in the db / db mice may be secondary to increased susceptibility to infections and resulting immune complex formation. Tohelp clarify the role of immune complex deposition in relation to therenal disease of db / db mice, immunofluorescentstudies in db / db mice raised in germ-freeenvironments will be necessary.2 |9 D  j- |1 _% m$ d0 X

VASCULAR AND TUBULOINTERSTITIUM

Advanced human diabetic nephropathy often exhibits arteriolarhyalinosis and tubular atrophy coupled with an increase in the interstitial volume ( 28 ). These features are largelyabsent in the db / db mouse kidney at 16 wk of age.At the more advanced age (21 wk), lesions suggestive of arteriolarhyalinosis (Fig. 1 C ) were noted. However, it has not beencharacterized whether both afferent and efferent arterioles aresimilarly affected. The tubular changes noted in the db / db mouse kidney primarily consist ofvacuolization of tubular cells (Fig. 1, B and C ).No evidence of tubular atrophy, tubulointerstitial fibrosis, oralterations of the medullary structure by light microscopy wasdiscernable. An overall increase in renal collagen content has beenreported in db / db mice ( 22 );however, comprehensive and sensitive studies of tubular and vasculardamage have not yet been published.
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RENAL FUNCTIONAL MEASUREMENTS (CLEARANCE STUDIES)8 u' t' w8 U) a

Given that the db / db mouse exhibits aprogressive increase in mesangial matrix expansion in the setting ofsevere hyperglycemia, it has been considered an appropriate model ofprogressive human diabetic nephropathy. As human diabetic nephropathyis initially characterized by a supernormal glomerular filtration rate(GFR) in the early stages and a decline in GFR in the later stages, measurements of GFR have also been assessed in db / db mice. GFR was repeatedly measured inconscious C57BL/6J db / db female mice andC57BLKS/J mice between 7 and 24 wk of age using single injections of 51 chromium-EDTA ( 8 ). As the GFR values weresimilar in both strains of db / db mice, the datawere pooled ( 8 ). GFR was found to be elevated in db / db mice as early as 7 wk of age, even thoughblood glucose levels were only mildly increased. Between 7 and 14 wk of age, the GFR was ~300µl · min 1 · mouse 1 in the control mice, whereas the GFR was ~700µl · min 1 · mouse 1 in the db / db mice. After 17 wk of age, the GFRremained constant in the nondiabetic mice; however, a markedvariability in the GFR was observed in the db / db mice, with some mice having GFRs below normal. This study concludedthat female db / db mice do hyperfilter at theonset of hyperglycemia and that GFR declines with the duration ofdiabetes. However, the GFR did not progressively increase in association with the severity of hyperglycemia and was similar in boththe BL6 and KSJBL6 mice strains.
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Recent studies used endogenous creatinine clearance in the db / db mouse model ( 4, 35 ) as anindex of renal function. At 8 wk of age, a twofold increase increatinine clearance in db / db male mice wasobserved ( 4 ). By 16 wk of age, the creatinine clearancewas reduced by 30-50% compared with age-matched control heterozygous mice ( 4, 35 ). Blood levels of creatininecorrespondingly increased by twofold in db / db mice at 16 wk of age ( 4, 35 ). Thus it appears that thepattern of creatinine clearance associated with the duration ofdiabetes in the db / db mouse corresponds well toactual GFR levels as reported by Gartner ( 8 ). However, by absolute values the calculated creatinine clearance in normal heterozygous mice was on the order of 60 µl · min 1 · mouse 1 ( 4 ), whereas the GFR was ~300µl · min 1 · mouse 1 by the 51 chromium-EDTA method ( 8 ).

The measurement of plasma or serum creatinine is quite problematic inmice ( 26, 27 ). Measurement of creatinine levels in normalmouse blood by Jaffé alkaline picrate reaction has yielded valuesranging from 17 to 106 µmol/l (0.2 to 1.2 mg/dl). However, theJaffé reaction has been reported to grossly overestimate theactual plasma creatinine concentration ( 26, 27 ). Theactual result based on an assay using HPLC provides values that areroughly one-third to one-fifth of the value found by the Jafféreaction in normal mice ( 27 ). Similar results were foundin db / db mice (Sharma and Dunn, unpublishedobservations). The increased concentration as measured by theJaffé reaction is thought to be due to the presence of yetunidentified noncreatinine chromagens present exclusively in mouseblood. Although several modifications of the Jaffé reaction havebeen touted to be more specific ( 7, 26, 31, 33 ), thesemeasurements have not been performed compared with HPLC. Presently,HPLC with either spectrophotometric (UV detection) or HPLC coupled to amass spectrometer appears to be the definitive method to measurecreatinine in mouse plasma or serum. Therefore, it is unclear what theendogenous creatinine clearance signifies in relation to renalfunction. Nevertheless, as prior studies have found that db / db mice do have an increase in serumcreatinine after the age of 16 wk ( 4, 35 ) and db / db mice older than 17 wk of age do have adecline in GFR ( 8 ), it may well prove correct that thetrue endogenous creatinine clearance reflects renal function. Formalstudies comparing creatinine clearance by HPLC-based methods withinulin-based GFR methods are presently underway to address this issuein diabetic mice.% a% s: C$ h' S

ALBUMINURIA

With the availability of sensitive and specific ELISAs formeasuring mouse albumin ( 6 ), levels of urinary albumin mayeasily be followed from mice placed in metabolic or diuresis cages.Several studies established that albumin excretion rates are higher by 8- to 62-fold in db / db mice beginning at the ageof 8 wk (Table 2 ). The range ofalbuminuria is between 68 and 303 µg/24 h in the db / db male mouse, whereas it is between 4 and 21 µg/24 h in the age-matched heterozygous littermate ( 4, 14 ). The degree of albuminuria does not consistently increasewith the duration of diabetes as there are similar levels ofalbuminuria at 8, 16, 21, and 25 wk ( 4, 9, 14, 35 ).
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Table 2. Albuminuria in C57BLKS/J Lepr (db/db and db/m) mice atvarious ages# Y  d$ _! s) C5 v1 H

Interestingly, when urinary protein was measured by a total proteinassay such as the Bradford reaction, no statistical increase in urinaryprotein was found in the 20-wk-old db / db mouse( 30 ). This would suggest that there is a selectiveincrease in albuminuria in the db / db mouse andthus can only be detected by an assay specific for albumin. Although ahead-to-head study has not been performed between db / db females and db / db males, the db / db males generally have twiceas much albuminuria compared with females ( 21 )(Sharma and Dunn, unpublished observations). In addition, inunpublished studies, we found that addition of a high-salt (5%) andhigh-protein (30%) diet led to a 50% increase in 24-h urinary albuminexcretion in db / db males.
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It is of interest that the increase in urinary albumin excretion hasbeen noted at 8 wk of age (Table 2 ), before the development of obviousstructural evidence of alterations of the GBM or the podocytes. By EMexamination, a mild segmental increase in GBM thickening and rarepodocyte foot process fusion has been noted at 16 wk of age( 11 ) (Sharma and Dunn, unpublished observations). Measurement of podocyte numbers as well as podocyte-specific proteins in relation to the development of albuminuria in the db / db mouse would be very informative.% K- t6 |7 x0 j6 _

BLOOD PRESSURE
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In the study by Koya et al. ( 14 ), blood pressure wasmeasured by the tail cuff method at the age of 16 wk in male db / m and db / db mice. Atthis time point, the mean blood pressure was 117 mmHg in db / m mice and 110 mmHg in db / db mice and not significantly different. Toour knowledge, no other studies reported blood pressure measurements inthe C57BLKS/J db / db mice.
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INSIGHTS FROM RECENT INTERVENTIONAL STUDIES
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On the basis of the recognition that the db / db mouse has many similar features of humandiabetic nephropathy, several studies were performed in this model toinvestigate the role of various candidate pathways in the progressionof diabetic renal disease. Studies by Cohen et al. ( 3, 6 )found that db / db mice have elevated glycatedalbumin and that antibodies against glycated albumin attenuatealbuminuria, mesangial matrix accumulation, and decline in renalfunction when given over a course of 8 wk. In addition, an oralinhibitor of Amadori glucose adducts maintained levels of glycatedalbumin in the normal range and exerted beneficial effects on featuresof diabetic nephropathy in the db / db mice ( 5 ). The role of PKC- in progressive diabetic kidneydisease has also been assessed in this model. Glomeruli from db / db mice at 25 wk of age were found to have atwofold increase in PKC activity ( 14 ). In db / db mice given an oral PKC- inhibitor from week 9 until week 25, normalization of glomerularPKC activity and significant reduction in albuminuria and mesangialmatrix expansion were observed ( 14 ).
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The role of antifibrotic approaches to inhibit progression of diabetickidney disease has also been demonstrated using the db / db mouse. The db / db mouse exhibits an increase in glomerular transforming growthfactor- 1 (TGF- 1 ) as well as an increase in the type II receptor for TGF- ( 11 ). InhibitingTGF-, with anti-TGF- antibodies, normalizes mesangial matrixaccumulation, gene expression for type IV collagen, and fibronectin, aswell as renal functional parameters ( 35 ). Interestingly, arecent study by Ziyadeh's group ( 2 ) found that mesangialmatrix changes in the db / db mouse appear to bereversible, as treatment of db / db mice withestablished disease decreased the extent of the lesions. The benefit ofanti-TGF- antibodies was found without a reduction in albuminuria inthe treated mice ( 35 ), suggesting that an anti-TGF- approach may be beneficial even without affecting albuminuria. In largepart due to the beneficial effect of inhibitors of various pathways inthe db / db mice, approaches to block glycatedproteins, PKC- activation, TGF- action, and renal fibrosis arepresently being considered as novel treatment strategies for humandiabetic nephropathy.
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In summary, the db / db mouse has a long history asa model of human diabetic nephropathy. Key common features with thehuman condition are renal hypertrophy, glomerular enlargement,albuminuria, and mesangial matrix expansion. Occasionally, arteriolarhyalinosis is observed in the glomerular arterioles. Features that arenot as reproducibly altered in the db / db mousewith respect to the human condition are the increase in GBM thickeningin relation to albuminuria and the lack of progressive increase inalbuminuria. Features that are not observed in the db / db mouse are the advanced features of diabeticnephropathy, such as nodular sclerosis in the glomeruli,tubulointerstitial fibrosis, and tubular atrophy. Features that may beinconsistent with human diabetic nephropathy include immune complexdeposition in the glomerulus and nodular thickening of thesubepithelial space. Improved methods to assess kidney function in the db / db mice are required to establish the extentof renal functional deterioration with duration of diabetes. Additionalstudies to examine the mechanisms underlying the development ofglomerular hypertrophy, albuminuria, and mesangial matrix expansion inthe db / db mouse could provide important insightand are likely to be of relevance to the development of human diabetic nephropathy.
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